Effect of camp agonists on cell ph and anion transport by cultured rat inner medullary collecting duct cells. Zhang, Chong, Russell F. Husted, and John B. Stokes. Laboratory of Epithelial Transport, Department of Internal Medicine, University of Iowa College of Medicine and Department of Veterans Affairs Medical Center, Iowa City, Iowa 52242
APStracts 2:0126F, 1995.
The rat inner medullary collecting duct is capable of secreting anions. We have previously shown that cAMP stimulates anion secretion; the apical membrane anion exit pathway activated by cAMP appears to be the cystic fibrosis transmembrane conductance regulator Cl- channel. The present experiments were designed to test the hypothesis that the entry pathway across the basolateral membrane is a Cl-/HCO3- exchanger operating in parallel with a Na+/H+ exchanger. We investigated the mechanism by measuring cell Cl-, cell pH, and short circuit current under a variety of conditions designed to uncover these pathways. Cyclic AMP agonists caused little change in cell Cl-, but they produced a consistent intracellular acidification. This acidification was dependent on HCO3-, but was not dependent on Cl- and was not inhibited by 4,4'-diisothiocyanatostilbene-2,2' -disulfonate (DIDS). The presence of the basolateral Cl-/HCO3- exchanger was demonstrated by several maneuvers and its activity was inhibited by DIDS. Applied to the basolateral solution, DIDS did not inhibit the cAMP-dependent anion current, but actually stimulated it. We conclude that cAMP-stimulated anion secretion does not require activation of the basolateral Cl-/HCO3- exchanger. The transporter responsible for Cl- entry across the basolateral membrane remains unknown and is not inhibited by a variety of anion transport inhibitors including DIDS, bumetanide, hydrochlorothiazide. The cell acidification induced by cAMP appears to be independent of acid secretion and is the result of activation of one or more HCO3- exit pathways that are resistant to DIDS, but are inhibited by a nonspecific anion transport inhibitor, 5-Nitro-2-(3 -phenylpropylamino)benzoic acid (NPPB). We present a revised model for anion transport by the rat IMCD. 

Received 5 April 1995; accepted in final form 17 July 1995.
APS Manuscript Number F116-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.